In recent years, as a wave length division multiplexing (WDM) transmission and an optical amplification technology progress, while an effective core area (Aeff) of an optical fiber has been scaled up, a more reduction of a polarization mode dispersion (PMD) characteristic has been desired. The polarization mode dispersion characteristic is caused by a transmission speed difference of optical signals between polarization waves perpendicular to each other, and depends on the symmetry of a refractive index distribution of the optical fiber. To be more specific, as the cross section shape of the refractive index distribution in a core portion (light propagation portion), through which a major part of light propagates, is closer to a perfect circle, the PMD characteristic in terms of the optical fiber itself becomes better. On the contrary, when the cross section shape thereof is uncircularized, the PMD characteristic becomes worse. Therefore, in the manufacture of the optical fiber, various contrivances for achieving a out-of-roundness of the cross section shape of the refractive index distribution in the core portion to acquire a good polarization mode dispersion characteristic have been made.